Masson staining was used to evaluate the extent of myocardial fibrosis and indicated that the collagen density in the infarcted area of the PCSK9−/− ischemia group was obviously decreased compared to the WT ischemia group (44.15 ± 8.38% vs. 25.32 ± 3.23%, P < 0.05) (Figures 2(e) and 2(f)). The gene discussed is PCSK9; the disease is Myocardial fibrosis.